Rotary engines burning gasoline are generally inefficient under lean conditions; spark ignition typically requires a homogeneous mixture of fuel and air near stoichiometric conditions in order to have sufficient combustion stability. Typically the fuel and air are premixed before being injected into the combustion chambers.
It is also known to use rotary engines with heavy fuel. A pilot subchamber can be used for pilot injection, which may allow for a lean fuel and air mixture to be used in the combustion chambers. The power output of such engines can however be limited by the maximum peak pressure allowable for the particular engine configuration.